There's Ellen DeGeneres, reprising her role as Dory, the energetic and forgetful Pacific regal blue tang. There's Ed O'Neill, making his debut as a surly septopus named Hank. Albert Brooks, Ty Burrell, Idris Elba, Bill Hader, Diane Keaton, Eugene Levy, Kate McKinnon, Kaitlin Olson, Bob Peterson, Hayden Rolence and Dominic West also lend their voice talents to the sequel. And then there's three-time Academy Award nominee Sigourney Weaver, whose disembodied voice welcomes visitors to the Marine Life Institute in Morro Bay, Calif. Weaver's recording is a running joke in the Disney•Pixar film, as the animals have all come to consider Weaver a friend.

If Weaver's inclusion seems random, that's because, well...it is.

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Before Finding Dory became a billion-dollar blockbuster, director Andrew Stanton and his creative team came upon a great gag. "We have a million ideas that are like that all day, that are either irreverent or R-rated or too risqué, too obscure, too odd, too niche. The nice thing is we have four years—so we try it out. We had Sigourney Weaver in there as a knee-jerk idea, because to me, I thought it was hilarious that you would hear a celebrity's voice," Stanton tells E! News. "She narrates a bunch of nature footage documentaries I own, and she's also the voice of the Arts and Sciences museum here in the Bay Area. So, I associated her with education and nature. Just the way her name sounds, it's so unique. It cracked us up."

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No one—Stanton included—expected the recurring joke to make the film. "We thought, 'This will just stay in our private version of the movie for about a year or two and it'll go away. This will never make it.'"

As time went on, the Weaver bit became more prominent. "Sometimes we keep things in the movie like that just to kind of remind us where the bar is set. Like, 'It better be as funny or funnier than Sigourney Weaver if we're going to have to find something else.' And we never could!" says Stanton, who also voices Crush the sea turtle. "As a matter of fact, the more people we showed it to and the farther the movie got along, the funnier it got. It got asked to be put in in other places in the film until we realized, 'We should make this integral to the film.'"

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There was just one problem: Weaver wasn't involved at that point.

So, before Stanton pitched the idea to Weaver, he needed to ensure that her scenes wouldn't end up on the cutting room floor. "Even then I was like, 'Sigourney Weaver is somebody I've worked with before. She's a friend. She's cinematic royalty. I am not going to ask her to do something like this unless I'm positive it's going to stay in the picture,'" he says. "I waited until I was eight months from release before I called her and kind of asked politely, 'Do you mind if we do this?' She has got such a great sense of humor and is such a team player. She totally went for it. I kind of warned her when we were recording, 'Kids are going to know your name because of this more than anything for the rest of your life—without even knowing your filmography.'"

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While Weaver's name will be forever embedded in Finding Dory, not every joke made the final cut—making the editing process as tricky as it was necessary. "You're constantly trying things. You're cutting things and putting things back, and it's very messy. It's like making up a recipe in a kitchen. We do the same thing, but on the front end with our storyboards, our voices and rewrites of our scripts. We do about six to seven re-shoots of our film before we're ever actually creating the footage, over the course of two to three years," Stanton says. "When we cut stuff out and when we put stuff back in is constantly happening, on an almost daily—weekly—basis."

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For example: a lengthier sequence involving the otters was whittled down for the theatrical release. In the end, Stanton says, it was the right choice. "We tried many versions, and it turned out that we just had too much screen time being spent with too many other characters other than Dory. And the strongest thing about the otters was that they were cute just to look at. If they didn't speak, we could have them onscreen without having to slow down the film and have a lot of dialogue," he says. "It allowed Fluke and Rudder, the two sea lions, to have more screen presence. And we learned that after doing so many tries with them over two, three years."

The animated movie was a labor of love—emphasis on the word "labor." And though he loved every moment of making Finding Dory, Stanton has no desire to direct a third underwater adventure. "I've spent eight years with fish. I really don't need to spend another four," admits Stanton, who previously directed 2003's Finding Nemo. "I'm hoping somebody else will pick up the mantle and run with it. Everybody wants Finding Hank—everybody I talk to! So, we'll see."

Finding Dory is available digitally Oct. 25 and on Blu-ray/DVD Nov. 15.